Electrolytic capacitors of this type have been hitherto constituted of an anode foil on which an anodized dielectric film is formed, comprising a high purity aluminum foil electrolytically etched to expand its effective areas and then subjected to formation treatment, and a cathode foil employing an aluminum foil electrolytically etched to expand its effective areas, which foils are wound interposing a separator followed by impregnation with a driving electrolyte (hereinafter "paste").
Such electrolytic capacitors used in commonly available electronic equipments are strongly demanded to be made more compact and thinner with the trend of making various electronic equipments more compact and thinner.
Incidentally, the capacitance C of electrolytic capacitors is the composite capacitance of the anode capacitance C.sub..sym. with the cathode capacitance C.sub..crclbar., and represented by the following formula: ##EQU1## Accordingly, it has been attempted to increase not only the electrostatic capacitance of the anode foil but also that of the cathode foil, but an excessive etching causes surface dissolution of aluminum foils to proceed and prevents the electrostatic capacitance from increasing, and also the etching resulting from non-uniform dissolution brings about an extreme lowering of foil strength, so that, since the foils are made to have smaller widths to make them compact, it has been further impossible to wind foils in a high speed, thus leaving a limit in increasing the electrostatic capacitance of cathode foils by using electrolytic etching techniques.
As a means for improving it, it is known to form a titanium-deposited film on the roughened surfaces of aluminum foils (for example, Japanese Unexamined Patent Publications No. 180420/1986 and No. 214420/1986).
The cathode foils obtained by such a titanium vacuum deposition process can have a greater surface area and a more increased electrostatic capacitance than those obtained by the electrolytic etching process, but have had the disadvantages that they have too dense a structure to be impregnated with the paste with ease and therefore the electrostatic capacitance can be effectively exhibited with difficulty as capacitors.
They also have had the disadvantage that a lowering of capacitance is caused when vacuum deposition is continuously carried out.